Speaking of concurrencies, Georgia actually ties the current record for most highways in a single concurrency (counting an unsigned highway). In Athens, US 29, US 78, US 129, US 441, GA 8, GA 10 Loop, GA 15, and the unsigned GA 422 travel in part of the city together.
Every Interstate highway in the state has an unsigned state route companion. Every U.S. Highway has at least one signed state route companion. There are so many concurrencies all across the state. In fact, there are lots of five-, six-, and seven-highway concurrencies mixed in.